October, 1911. 



KNOWLEDGE. 



409 



GROUSE AND DISEASE.— Supplementing the note on 

 page J55 ante, it should perhaps be said that Dr. Shipley, in 

 the Report, explains that in the course of their researches 

 during the inc|uiry, the investigators did not come across the 

 "disease," which is so firmly believed in by sportsmen and 

 gamekeepers. Twenty-three parasites of the grouse were 

 found, and Dr. Slnplc\- writes of the worm Tricliosti'ongylns 

 pcrgrcTcilis as follows: — "The eggs give rise to larvae in about 

 two da\'s. The larvae surround themsehes about the eighth 

 day with a capsule or cyst, and undergo a ' rest cure.' After 

 a period of cjuiescence they quickly change into second and 

 active larval forms, which are minute, transparent, and quite 

 invisible. These lead a perfectly free life, and in wet weather 

 gradually siiuirm and crawl up among the leaves and flowers 

 of the heather, where they remain until swallowed by the 

 grouse. When once inside the bird, the larvae make their way 

 along the alimentary track, and enter the caeca, where they 

 rapidly develop into adults." Dr. Shipley also presents a 

 word-picture of what would be seen. if. by means of a gigantic 

 lens, a square yard of grouse moor were magnified a hundred 

 times : — " The heather plants would be as tall as lofty elms, 

 their flowers as big as cabbages, the grouse would be si.x or 

 seven times the size of 'Chantecler" at the Porte St. Martin. 

 Creeping and wriggling up the stem and over the leaves, and 

 gradually yet surely making their way towards the flowers, 

 would be seen hundreds and thousands of silvery white worms 

 about the size of young earth-worms. Lying on the leaves 

 and on the plant generally would be seen thousands of 

 spherical bodies the size of grains of wheat, the cysts of the 

 coccidium ; and on the ground and on the plants, as large as 

 split peas, would be seen the tapeworm eggs patiently awaiting 

 the advent of their second host. It is perhaps a picture that 

 will not appeal to All, yet it represents what, unseen and 

 unsuspected, is always going on upon a grouse moor." — See 

 " The Grouse in Health aTid Disease ; being the final Report 

 of the Conunittee of Inquiry on (~irousc Disease." Two 

 volumes. Illustrated. London, loll. 



MORE ABOUT THE CORN-CRAKE.— The distribution 

 of this species {Crcx pratciisis). in England continues to call 

 forth observations, and Mr. I-'. J. Stubbs has some apt remarks 

 in 7'lic Zoologist for August. 1911 (page 315). He points out 

 that the disappearance of the species from the south-eastern 

 counties of England dates from about 1850, and ascribes this 

 to the change in agricultural methods that was in course then. 

 The bird formerly bred in the corn-fields of the southern 

 counties, which, under the old system of broadcast sowing, 

 would be a real sanctuary. In a drilled cornfield this is not 

 so ; the nest could not be hidden and would be an easy prey 

 to stoats. For this reason, and as the meadows are also 

 unsafe and pasture fields inadequate, the bird has practicallv 

 vanished as a nesting species. 



The curious annual fluctuations of the bird are conunented on 

 by Mr. Stubbs, who says that the present year nuist be 

 reckoned a corn-crake year in Lancashire, the species ha\'i[ig 

 been commoner than for many seasons. 



In the recently published " Fauna of the Tweed .\rea " 

 (1911), Mr. A. H. Evans reports that the bird is stated to be 

 decreasing in some localities there, but that it is sulificiently 

 plentiful in most parts. It is somewhat local, and almost 

 absent from the coast-lands where there are few grass fields, 

 but is common, not only in the lower valleys, but among the 

 hills in " Tweed." 



PHYSICS. 



By Ar.i'KEi) C. G. Egekto.v, B.Sc. 



INAUDlBLi: SOUNDS.— The Umit of perception of 

 sounds of high pitch varies with the person. In general, 

 persons lose their hearing for very high notes as they get 

 older, and it appears that slight loss of hearing in the region 

 of these upper frequencies begins to occur during quite an 

 early age. Many cannot hear the sound of the bat squeaking, 

 or of certain insects. Very acute sounds are audible up to 



thirty-eight thousand vibrations per second. Helmholtz gave 

 as the lower limit, thirty \ ibrations per second, and a regular 

 wave train of forty vibrations per second was the lowest 

 musical note. Thus the ear can perceive vibrations ranging 

 from thirty to thirty-eight thousand per second. No doubt 

 higher sounds are common in nature : it is probable that 

 animals have different ranges of perceptin;i. Many persons 

 with average powers of hearing may be deaf to vibrations of 

 thirteen thousand per second. In this connection it is 

 interesting to note that old people often lack the ability to 

 distinguish the letter " s " distinctly ; the telephone and the 

 phonograph also have difficulty in transmitting that letter. 

 Now, the hissing sound when analysed into a wave form is a 

 succession of waves with very minute irregularities on the face 

 of the wa\es, and thus is equivalent in its facility to detection 

 to a sound of very high pitch. Campbell and Dye have 

 published, in Tlw Electrician, iin account of some work on the 

 detection of inaudible sounds. The electric spark gives out 

 waves of sound which are exceedingly short and far too high- 

 pitched to be audible. The means by which the frequencies 

 of these sound waves are measured are very simple. The 

 oscillatory spark is arranged at the open end of a long 

 horizontal glass tube along which is shaken out a little 

 clyopodium powder. As the sound waves progress along the 

 tube they set the lycopodium in motion, taking it away from 

 the positions of least movement (the nodes) and laying it about 

 where the air is in a greater state of turmoil. It is, in fact, the 

 " Kundt's tube " arrangement which has been used to find the 

 velocity of sound in various gases ; for, by measuring the 

 distance between the small heaps of dust produced b\- the 

 particular note, the wave lengths can be foiuid and hence the 

 velocity (for the velocity equals the product of the freijuency 

 of vibration and the wave length). The method has various 

 applications, for, from the velocity, the ratio of the amount of 

 heat a gas can take up when free to expand and when con- 

 fined can be found, and from this again whether the gas 

 consists of a molecule possessing internal energy besides 

 translation, or merely ener.gy of translation : in the latter case 

 the molecule consists of one atom. In this way the molecules 

 of argon, heliunr, krypton, xenon, neon and mercury have 

 been found to be monatomic. That is, the molecular weights 

 equal the atomic weights. Campbell and Dye measured the 

 distance between the striations produced in the lycopodium 

 dust along the tube and found that they could measure in this 

 way sounds of a frequency up to eight hundred thousand per 

 second ; their results seem to show that, since two sound 

 waves are given out for each oscillation, the sound vibrations 

 are double the frequency of the electrical oscillations. 



THE AMPALL. — A few months back I mentioned this as 

 one of the novelties in electrical instrument design which ha\e 

 been elaborated by Messrs. Paul. The instrument consists of 

 a moving coil unipivot gahanometer connected to a pair of 

 contact points a definite distance apart, such that if placed on 

 a copper conductor of one square inch in cross section a read- 

 ing of one thousand t = 2 millivolts) is obtained, if one 

 thousand amperes are flowing through the wire. The contact 

 block is strapped to the conductor, the cross section of which 

 multiplied by the deflection of the unipivot millivoltmeter gives 

 the current in amperes. The instrument can be used to 

 measure direct currents up to any value and can be instantly 

 applied without breaking the circuit ; it also provides a means 

 of testing the conductivity of joints, fuses and so on. 



The unipivot system of suspension of the gahanometer 

 needle is very satisfactory, as it allows of great sensitiveness 

 with perfect portability. The moving coil has one pivot only 

 in the centre of a sphere of iron. The circular coil swings 

 freely about this sphere without touching the magnetic system. 

 .A circular well aged magnet is so situated that the field is 

 concentrated across the gap where the sphere resides. The 

 pivot is situated at the geometric centre of the coil, which is 

 also the centre of gravity of the moving system. The arrange- 

 ment, residing on the one pivot and held in position only by 

 a hair spring, is thus capable of considerable sensitiveness : 

 while the protection afforded by the sphere to the coil, pivot 



